As such a gland packing, conventionally, known is a die mold packing 51 having a usual structure shown in FIG. 25. The die mold packing 51 is configured by windingly laminating a tape-like material 50 such as an expanded graphite tape into a spiral shape, and then die-molding the lamination into a ring-like shape. Such a die mold packing 51 is used in the following manner. As shown in FIG. 26, in a stuffing box 54, the die mold packings 51, and a plurality of laminate packings 53 which are obtained by laminating ring-like sheet materials 52 having impermeability are alternately disposed on the outer periphery of a shaft or a valve rod 55 (hereinafter, referred to as “valve rod or the like”) in an axial direction. Alternatively, as shown in FIG. 27, the die mold packings 51, and braided packings 56 which are well known in the art are combinedly disposed. These packings are pressed in the axial direction through a packing gland 57 so that their inner peripheral face parts are brought into tight contact with the outer peripheral face of the valve rod or the like 55, thereby performing the shaft sealing operation.
Furthermore, also a gland packing 58 is known in which, as shown in FIG. 28, a ring-like projected part 51a is formed on an end face in an axial direction of the die mold packing 51 and in an outer end portion in a radial direction so that the ring-like projected part is projected outward in the axial direction, and a ring-like recess 56a which is formed on an end face in the axial direction of the braided packings 56 and in an outer end portion in a radial direction is fitted onto the ring-like projected part 51a, thereby integrating the packings 51 and 56 into one body. Also the integrated gland packing 58 is used in the following manner. As shown in FIG. 29, the integrated gland packings 58 are combinedly disposed in the stuffing box 54 together with the die mold packings 51 having the ring-like projected part 51a. In the same manner as described above, these packings are pressed in an axial direction through the packing gland 57 so that their inner peripheral face, parts are brought into tight contact with the outer peripheral face of the valve rod or the like 55, thereby performing the shaft sealing operation.
In a prior art gland packing mainly consisting of the die mold packings 51, as shown in FIGS. 25 and 28, minute gaps 59 are inevitably formed in windingly laminated parts of the tape-like material 50. A pressurized fluid penetrates into the minute gaps 59, and leakage indicated by the arrow a easily occurs. Particularly when a gas fluid of low molecular weight flows through the hydraulic machine, it is very difficult to prevent penetration leakage from occurring.
Furthermore, the die mold packing 51 which is configured by windingly laminating the tape-like material 50 has originally a lower strength. In a use manner, the die mold packing is disposed in substantially parallel to the axis of the valve rod or the like 55. When the material is pressed in an axial direction, the material is swollen out to enter the gaps so that stress relaxation easily occurs. Furthermore, the process of the die molding is conducted at a high face pressure. When the die mold has a rectangular section shape, therefore, the die mold cannot exhibit sufficient sealing performance at a low tightening force.
Moreover, when the die mold packings 51 and the laminate packings 53 are combinedly used as shown in FIG. 26, the amount of deformation of the laminate packings 53 in the pressurizing process is small, and hence the laminate packings 53 must be produced with very high dimensional accuracy. Furthermore, the parts of the laminate packings 53 are easily worn. Even when the parts are worn at a very small amount, the contact surface pressure acting on the valve rod or the like 55 is extremely lowered, thereby producing a problem in that sealing performance is largely impaired.
The invention has been conducted in view of the above-mentioned circumstances. It is an object of the invention to provide a gland packing which can prevent penetration leakage from occurring, which can be sufficiently deformed so as to exhibit sure sealing properties even at a low tightening force, and which has following properties against a small amount of wear so as to ensure high sealing performance for a long term.